Low approaches in ground effect

[CV]

First a disclaimer: I understand the security issues involved
in the following and would not encourage anyone to try this
at home, but I am interested in the theoretical side of it.

Imagine you get things wrong and are caught out low on final,
still a fair distance out, and it looks marginal whether you
are going to reach the runway or not.

One technique I have sometimes heard described is to dive for
the deck and complete the remaining distance in ground effect.
For the sake of the argument we can assume fairly flat ground,
free of obstacles, though not necessarily landable.

The advantages claimed are usually better glide performance in
ground effect and less headwind and absence of downdrafts close
to the ground.

On the other hand you'll be travelling at higher than optimal
airspeed for most of the distance.

I am wondering how much truth there actually is to this
technique. Would it significantly increase your range and
improve your chances of reaching the field or not ?

Would it perhaps work better against a strong wind gradient
(as I suspect it might), and maybe not help a lot in calm
conditions ?

I'd be interested in any hard data/analysis or otherwise
enlightening comments on this.

Please note though, that I am not talking about high-speed
competition finishes, rounded off with a beatup and a sharp
pullup and all the dangers and other issues involved in that.

Cheers CV

[Dave Martin]

Don't know whether this answers your question!

A Russian airforce pilot perfected this technique for
getting home on minimum fuel using ground effect to
prolong his flights. His ideas were developed into
ground effect vehicles which the Russians built in
a variety of forms.

The largest being the size of 747's and were named
the Caspian Sea Monsters. The intended development
was for military use. the end of the cold war stopped
production of the big ones. Some smaller craft have
been produced.

Briefly the idea is that you force air under the craft
with huge forward mounted jet engines, which provide
both the air cushion and thrust. Not quite the same
as just using ground effect to prolong an approach!

Ground effect does work with a low wing glider, other
than using the effect to float along way across flat
airfields I have never used it to prolong a final glide
over rough ground. But practice suggest that you have
to be very low to get the best effect and is only short
lived. A few hundred yards rather than miles, but then
I have never tried to go miles.

For Kranoplan information see

See http://aeroweb.lucia.it/~agretch/RAFAQ/WIG.html

>First a disclaimer: I understand the security issues
>involved
>in the following and would not encourage anyone to
>try this
>at home, but I am interested in the theoretical side
>of it.
>
>Imagine you get things wrong and are caught out low
>on final,
>still a fair distance out, and it looks marginal whether
>you
>are going to reach the runway or not.
>
>One technique I have sometimes heard described is to
>dive for
>the deck and complete the remaining distance in ground
>effect.
>For the sake of the argument we can assume fairly flat
>ground,
>free of obstacles, though not necessarily landable.
>
>The advantages claimed are usually better glide performance
>in
>ground effect and less headwind and absence of downdrafts
>close
>to the ground.
>
>On the other hand you'll be travelling at higher than
>optimal
>airspeed for most of the distance.
>
>I am wondering how much truth there actually is to
>this
>technique. Would it significantly increase your range
>and
>improve your chances of reaching the field or not ?
>
>Would it perhaps work better against a strong wind
>gradient
>(as I suspect it might), and maybe not help a lot in
>calm
>conditions ?
>
>I'd be interested in any hard data/analysis or otherwise
>enlightening comments on this.
>
>Please note though, that I am not talking about high-speed
>competition finishes, rounded off with a beatup and
>a sharp
>pullup and all the dangers and other issues involved
>in that.
>
>Cheers CV
>
>

[CV]

Dave Martin wrote:
> Don't know whether this answers your question!

No bearing on the question, really, though it is
slightly related, and interesting as well.

> Ground effect does work with a low wing glider, other

I don't know of any low-wing gliders. Most are mid-wing
and some older types are high-wing, but that difference
is so small I wouldn't expect it to matter. In the
situation I asked about we'd want a safety margin
of perhaps 5 feet or so off the ground in any case.

AFAIK ground effect starts being significant from
approx. half a wingspan off the ground, the effect
being to increase performance, as if you had greater
span.

> lived. A few hundred yards rather than miles, but then
> I have never tried to go miles.

A few hundred yards would be sufficient for what I had
in mind, provided that the other factors balanced out
and resulted in a net gain in how far you can glide.

Cheers CV

[Bill Daniels]

"CV" > wrote in message
...
>
> Dave Martin wrote:
> > Don't know whether this answers your question!
>
> No bearing on the question, really, though it is
> slightly related, and interesting as well.
>
> > Ground effect does work with a low wing glider, other
>
> I don't know of any low-wing gliders. Most are mid-wing
> and some older types are high-wing, but that difference
> is so small I wouldn't expect it to matter. In the
> situation I asked about we'd want a safety margin
> of perhaps 5 feet or so off the ground in any case.
>
> AFAIK ground effect starts being significant from
> approx. half a wingspan off the ground, the effect
> being to increase performance, as if you had greater
> span.
>
> > lived. A few hundred yards rather than miles, but then
> > I have never tried to go miles.
>
> A few hundred yards would be sufficient for what I had
> in mind, provided that the other factors balanced out
> and resulted in a net gain in how far you can glide.
>
> Cheers CV

The rule I learned was that ground effect became measurable at one wingspan
above the ground and near the ground could double the L/D. Running in
ground effect is a lot of fun but you'd better be very smooth on the
elevator since the pitch control gets 'twitchy'.

(I strongly suspect that unanticipated elevator sensitivity in ground effect
is a secondary cause of some of the G103 "PIO" accidents.)

The best glide stretching technique is to approach the ground at slightly
better than best L/D speed leveling off a couple of feet above the ground.
Diving to the ground is dangerous and wastes energy that could better be
spent at best glide. Maintaining the usual approach speed seems to work
best.

Of course, all this assumes that the approach and runway under-run are
completely free of obstacles like wires or fences.

Bill Daniels

[JC]

On Mon, 18 Oct 2004 16:13:41 +0200, CV > wrote:

>
>First a disclaimer: I understand the security issues involved
>in the following and would not encourage anyone to try this
>at home, but I am interested in the theoretical side of it.
>
>Imagine you get things wrong and are caught out low on final,
>still a fair distance out, and it looks marginal whether you
>are going to reach the runway or not.
>
>One technique I have sometimes heard described is to dive for
>the deck and complete the remaining distance in ground effect.
>For the sake of the argument we can assume fairly flat ground,
>free of obstacles, though not necessarily landable.
>
>The advantages claimed are usually better glide performance in
>ground effect and less headwind and absence of downdrafts close
>to the ground.
>
>On the other hand you'll be travelling at higher than optimal
>airspeed for most of the distance.
>
>I am wondering how much truth there actually is to this
>technique. Would it significantly increase your range and
>improve your chances of reaching the field or not ?
>
>Would it perhaps work better against a strong wind gradient
>(as I suspect it might), and maybe not help a lot in calm
>conditions ?
>
>I'd be interested in any hard data/analysis or otherwise
>enlightening comments on this.
>
>Please note though, that I am not talking about high-speed
>competition finishes, rounded off with a beatup and a sharp
>pullup and all the dangers and other issues involved in that.
>
>Cheers CV


I demonstrate to my students ground effect by approaching a 4200 foot
runway in a Blanik L-13 at about 55-60 knots. I would be at the
threshold a foot above ground. I could float over 3500 feet before I
would settle down and use the wheel brake to avoid running off the end
of the field. It is very effective. (There was little or no wind
when I did this.)

I once had to use this technique when I allowed myself to be
distracted on base leg. When I turned final I realized I was too low
to make the field but had plenty of speed. I dove toward the ground,
and put the glider in ground effect and made the field. (There were no
obstructions.)

A fellow instructor referred to ground effect as the last refuge of
the scoundrel glider pilot.

[nafod40]

Bill Daniels wrote:
>
> The rule I learned was that ground effect became measurable at one wingspan
> above the ground and near the ground could double the L/D. Running in
> ground effect is a lot of fun but you'd better be very smooth on the
> elevator since the pitch control gets 'twitchy'.
>
> (I strongly suspect that unanticipated elevator sensitivity in ground effect
> is a secondary cause of some of the G103 "PIO" accidents.)

Interesting observation. Flying in ground effect places the center of
pressure of the wing at about mid-chord, while out of ground effect the
center of pressure is about 1/4 chord. So in short, ground effect
usually has a stabilizing effect by essentially shifting the CG forward
with respect to the center of lift.

[Bill Daniels]

"nafod40" > wrote in message
...
> Bill Daniels wrote:
> >
> > The rule I learned was that ground effect became measurable at one
wingspan
> > above the ground and near the ground could double the L/D. Running in
> > ground effect is a lot of fun but you'd better be very smooth on the
> > elevator since the pitch control gets 'twitchy'.
> >
> > (I strongly suspect that unanticipated elevator sensitivity in ground
effect
> > is a secondary cause of some of the G103 "PIO" accidents.)
>
> Interesting observation. Flying in ground effect places the center of
> pressure of the wing at about mid-chord, while out of ground effect the
> center of pressure is about 1/4 chord. So in short, ground effect
> usually has a stabilizing effect by essentially shifting the CG forward
> with respect to the center of lift.
>
Al I can say is put a G103 in ground effect and see for yourself.
Obviously, flying qualities in ground effect deals with the whole glider and
not just the wing. No doubt the flow over the tail is involved as well.

Bill Daniels

[nafod40]

Bill Daniels wrote:
> "nafod40" > wrote in message
>>
>>Interesting observation. Flying in ground effect places the center of
>>pressure of the wing at about mid-chord, while out of ground effect the
>>center of pressure is about 1/4 chord. So in short, ground effect
>>usually has a stabilizing effect by essentially shifting the CG forward
>>with respect to the center of lift.
>>
>
> Al I can say is put a G103 in ground effect and see for yourself.
> Obviously, flying qualities in ground effect deals with the whole glider and
> not just the wing. No doubt the flow over the tail is involved as well.

I have, and i don't remember any decrease in longitudinal stab. Having
the ground that close certainly tends to "up the gain" in the soft mushy
grey matter autpilot though.

[John Cochrane]

> Imagine you get things wrong and are caught out low on final,
> still a fair distance out, and it looks marginal whether you
> are going to reach the runway or not.
>
> One technique I have sometimes heard described is to dive for
> the deck and complete the remaining distance in ground effect.
> For the sake of the argument we can assume fairly flat ground,
> free of obstacles, though not necessarily landable.


A few years ago Soaring Magazine reported experiments on this
undertaken (I believe) by the airforce glider program. They used
Blaniks and a very long runway. The conclusion was that it was better
to stay at max glide and not dive for the ground. I forget though how
much wind they had -- there is some headwind (50 mph) and gradient (to
zero at ground level) where it has to be better to dive. And Blaniks
are pretty bad at high speed -- though will have more induced drag at
any speed in ground effect too.

John Cochrane BB

[Mark Grubb]

> One technique I have sometimes heard described is to dive for
> the deck and complete the remaining distance in ground effect.
> For the sake of the argument we can assume fairly flat ground,
> free of obstacles, though not necessarily landable.
>
> >
> Would it perhaps work better against a strong wind gradient
> (as I suspect it might), and maybe not help a lot in calm
> conditions ?
>
> I'd be interested in any hard data/analysis or otherwise
> enlightening comments on this.
>

USAF Test Pilot School Candidates did this as a student project 10 yrs
+/- ago. Used a G103 and found that one was definitely better off
flying speed-to-fly u\into ground effect and then leveling off.
Probably diving down would be better in a strong wind gradient but
determining the gradient and what speed-to-fly through it would be
operationally very difficult.

You could probably get a copy of the report from USAF TPS at Edwards,
CA.

[COLIN LAMB]

An additional concern to those who dive to go into ground effect is that you
are giving up the ability to choose a touchdown point. Once in ground
effect, the pilot loses the ability to turn and must touch down straight
ahead. Altitude, however, gives the pilot the option of turning slightly to
avoid something hard.

If you cannot make the airport, pilots must select the best option as soon
as possible, using the aircraft as a bargaining chip. Walking away is the
concern rather than making the airport. From that standpoint, altitude
gives us the most options for the longest time.

Colin N12HS


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[Daniel]

> >First a disclaimer: I understand the security issues involved
> >in the following and would not encourage anyone to try this
> >at home, but I am interested in the theoretical side of it.
> >
> >Imagine you get things wrong and are caught out low on final,
> >still a fair distance out, and it looks marginal whether you
> >are going to reach the runway or not.
> >
> >One technique I have sometimes heard described is to dive for
> >the deck and complete the remaining distance in ground effect.
> >For the sake of the argument we can assume fairly flat ground,
> >free of obstacles, though not necessarily landable.
> >
> >The advantages claimed are usually better glide performance in
> >ground effect and less headwind and absence of downdrafts close
> >to the ground.
> >
> >On the other hand you'll be travelling at higher than optimal
> >airspeed for most of the distance.
> >
> >I am wondering how much truth there actually is to this
> >technique. Would it significantly increase your range and
> >improve your chances of reaching the field or not ?
> >
> >Would it perhaps work better against a strong wind gradient
> >(as I suspect it might), and maybe not help a lot in calm
> >conditions ?
> >
> >I'd be interested in any hard data/analysis or otherwise
> >enlightening comments on this.
> >
> >Please note though, that I am not talking about high-speed
> >competition finishes, rounded off with a beatup and a sharp
> >pullup and all the dangers and other issues involved in that.
> >
> >Cheers CV
>

CV, a group of test pilot trainees at Edwards AFB did an exhaustive
test on ground effect versus distance as a project during their
course; it was reported in the Feb 1990 SOARING magazine. IIRC, they
found that one had to fly a very precise profile - 0.95g push followed
by 1.05g pull, to a precise height - to see any measurable effect, and
concluded that it was better for the casual flier to fly best
lift/drag speed instead... I think they used a G103. The notation
from the index is:
Hadfield, Chris; with Chuck Louie, Ken Green, Rick Husband and Nate
Jones Is Ground Effect Worth It? [Aerodynamics], February, page 33

Chris Hadfield was a Canadian mission specialist on the Shuttle; two
flights, two spacewalks; top test pilot of his class at Edwards; and
US Navy Test Pilot of the Year for a F/A-18 out of control recovery
test program; Rick Husband was the crew commander on Columbia which
was destroyed on re-entry in Feb 2003, his second shuttle flight.

It might be worth getting the article reprint if you're interested in
the theory, or e-mail Edwards Test Pilot School for the report; I bet
it's swimming in math! IF you do, let us know how good my memory held
up.
DD

[Gerhard Wesp]

nafod40 > wrote:
> Interesting observation. Flying in ground effect places the center of
> pressure of the wing at about mid-chord, while out of ground effect the

Are you sure? Note that a forward CG implies a pitch down moment which
would have to be compensated by negative lift on the tail. Hence
performance degradtation, contrary to what ground effect is supposed to
create.

I'm still searching for a good explanation of ground effect :-)

Cheers
-Gerhard
--
Gerhard Wesp o o Tel.: +41 (0) 43 5347636
Bachtobelstrasse 56 | http://www.cosy.sbg.ac.at/~gwesp/
CH-8045 Zuerich \_/ See homepage for email address!

[Dave Martin]

FWIW Earlier I said this effect worked better with
low wing gliders. Bill Daniels queried low wing, Bill
I stand corrected!

My only experiences are with Ask 4's and Ask7(high
wing) many years ago and later ASK13, Grob and Puchacz.
As Bill correctly says these later ones are mid wing
rather than low wing, however the effect appears more
marked with the mid wing gliders than the higher ones.

Gethard, for a better explanation see

http://www.se-technology.com/wig/index.php

where there is both a description and pictures.


At 11:06 19 October 2004, Gerhard Wesp wrote:
>nafod40 wrote:
>> Interesting observation. Flying in ground effect places
>>the center of
>> pressure of the wing at about mid-chord, while out
>>of ground effect the
>
>Are you sure? Note that a forward CG implies a pitch
>down moment which
>would have to be compensated by negative lift on the
>tail. Hence
>performance degradtation, contrary to what ground effect
>is supposed to
>create.
>
>I'm still searching for a good explanation of ground
>effect :-)
>
>Cheers
>-Gerhard
>--
>Gerhard Wesp o o Tel.: +41 (0)
>43 5347636
>Bachtobelstrasse 56 | http://www.cosy.sbg.ac.at/~gwesp
>>/
>CH-8045 Zuerich \_/ See homepage for
>email address!
>

[nafod40]

Gerhard Wesp wrote:
> nafod40 > wrote:
>
>>Interesting observation. Flying in ground effect places the center of
>>pressure of the wing at about mid-chord, while out of ground effect the
>
>
> Are you sure? Note that a forward CG implies a pitch down moment which
> would have to be compensated by negative lift on the tail. Hence
> performance degradtation, contrary to what ground effect is supposed to
> create.

That part would be minor, more than compensated for by decrease in
induced drag and increase in lift.

> I'm still searching for a good explanation of ground effect :-)

Here's a killer page describing the aerodynamics of it. Follwoing is a
short excerpt from the page.
http://www.se-technology.com/wig/html/main.php?open=aero&code=0

Two phenomena are involved when a wing approaches the ground. Ground
effect is one name for both effects which is sometimes confusing. The
two phenomena are sometimes referred to as span dominated and chord
dominated ground effect. The former results in a reduction of induced
drag (D) and the latter in an increase of lift (L). The overall effect
is an increase of the L/D ratio. This ratio is a measure for the
efficiency of an aircraft which can be expressed as the amount of power
(thrust) that is required to propell an aircraft of a certain weight.
Since thrust is equal to drag and weight is equal to lift in stationary
flight this efficiency can be expressed as the L/D ratio. As the L/D of
a wing increases with decreasing ground clearance the craft becomes more
efficient in ground effect.

[COLIN LAMB]

The Hughes HK-1 Flying Boat (commonly and mistakenly called the Spruce Goose
since those closer to the project called it the Birch Bitch) was designed to
fly the entire flight in ground effect. It is displayed a short distance
from my home. When first acquired by Evergreen Museum, consideration was
given to fly it to the new home. However, the local fire marshall had
required a fire retardant to be sprayed on the aircraft before it was
originally put on display and that forever destroyed the ability to fly.

Now that would have been a sight to behold - the HK-1 soaring the Sierra
Nevadas in a Wave.

Colin N12HS


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[Bill Daniels]

"COLIN LAMB" > wrote in message
nk.net...
> The Hughes HK-1 Flying Boat (commonly and mistakenly called the Spruce
Goose
> since those closer to the project called it the Birch Bitch) was designed
to
> fly the entire flight in ground effect. It is displayed a short distance
> from my home. When first acquired by Evergreen Museum, consideration was
> given to fly it to the new home. However, the local fire marshall had
> required a fire retardant to be sprayed on the aircraft before it was
> originally put on display and that forever destroyed the ability to fly.
>
> Now that would have been a sight to behold - the HK-1 soaring the Sierra
> Nevadas in a Wave.
>
> Colin N12HS
>
>

Actually, Hughes wanted the HK-1 to use 8 Lycoming R-7755's but was forced
by the government to use much less powerful Pratt & Whitney R-4360's. With
8 7000 HP Lyc's the HK-1 would have cruised in the stratosphere at a very
respectable speed for the time. With the Pratts, all it could do was fly in
ground effect.

The Northrop B-35 flying wing was also supposed to get the R-7755 but the
then Secretary of War owned a huge block of stock in P&W.

The Smithsonian Air & Space Museum has placed the only remaining R-7755 on
prominent display at Udvar-Hazy Center without political comment. The
Lycoming engineers were confident that the R-7755 could be developed to
produce 10,000 HP.

Bill Daniels

Bill Daniels

[John Sinclair]

Bill,
If memory serves me right the 4360 had 4 rows of 9
cylinders for a total of 36 jugs. The aft rows were
spiraled to allow cooling to the rear rows, but even
so, the fourth row would run hotter. (KC-97F --circa
1952)
What was the configuration of the 7755?



At 13:48 19 October 2004, Bill
>Lycoming engineers were confident that the R-7755 could
>be developed to
>produce 10,000 HP.

[Nyal Williams]

Uh-Oh!


We've just discovered this winter's discussion topic.
For what it's worth, Gale Craig, a physicist in Anderson,
IN, has written a book titled, I believe, Why Airplanes
Fly, in which he analyzes ground effect. He derives
his theories from Newton rather than from Bernouilli.
It is an interesting read.

A second edition had the title changed to something
like, Don't Abuse Bernouilli. The book is published
privately and has been reviewed on the web. I can
supply an address and telephone number to anyone interested.


At 11:06 19 October 2004, Gerhard Wesp wrote:
>nafod40 wrote:
>> Interesting observation. Flying in ground effect places
>>the center of
>> pressure of the wing at about mid-chord, while out
>>of ground effect the
>
>Are you sure? Note that a forward CG implies a pitch
>down moment which
>would have to be compensated by negative lift on the
>tail. Hence
>performance degradtation, contrary to what ground effect
>is supposed to
>create.
>
>I'm still searching for a good explanation of ground
>effect :-)
>
>Cheers
>-Gerhard
>--
>Gerhard Wesp o o Tel.: +41 (0)
>43 5347636
>Bachtobelstrasse 56 | http://www.cosy.sbg.ac.at/~gwesp
>>/
>CH-8045 Zuerich \_/ See homepage for
>email address!
>

[Buck Wild]

John Sinclair > wrote in message >...
> Bill,
> If memory serves me right the 4360 had 4 rows of 9
> cylinders for a total of 36 jugs. The aft rows were
> spiraled to allow cooling to the rear rows, but even
> so, the fourth row would run hotter. (KC-97F --circa
> 1952)
> What was the configuration of the 7755?


http://www.aviation-history.com/engines/xr-7755.html

-Dan

[Buck Wild]

John Sinclair > wrote in message >...
> Bill,
> If memory serves me right the 4360 had 4 rows of 9
> cylinders for a total of 36 jugs. The aft rows were
> spiraled to allow cooling to the rear rows, but even
> so, the fourth row would run hotter. (KC-97F --circa
> 1952)
> What was the configuration of the 7755?

http://www.enginehistory.org/NASM/Lycoming%20XR-7755.jpg
-Dan
>
>
>
> At 13:48 19 October 2004, Bill
> >Lycoming engineers were confident that the R-7755 could
> >be developed to
> >produce 10,000 HP.

[Andre van Niekerk]

I was flying a Ka 7 in a very strong wind condition. At stall speed up wind
it appeard to have no forward ground speed. At 900ft above ground i started
my circuit and at about 700 ft on downwind i passed the start of the runway
and did a base and finals in a slow turn. At finals i looked down to the
start of the runway at about 45degrees. The wind blow me past the runway
(downwind) aprox 300 meters. I realized that i would not make it back at my
rate of decent and forward motion.Before me was nowhere to land as it was
only threes . I decided to change my alltitude for speed and out of the
headwind and into ground effect. The last few moment was nailbiting as i had
to get over 2 fences and a road but made it. My point: If there is no
headwind it will be better to approach at beast glide angle as ground effect
will be slightly cancelled by profile drag due to higer speed. If you have a
strong head wind it will help to get out of the wind and use ground affect.

Regards

Andre

"CV" > wrote in message
...
>
> First a disclaimer: I understand the security issues involved
> in the following and would not encourage anyone to try this
> at home, but I am interested in the theoretical side of it.
>
> Imagine you get things wrong and are caught out low on final,
> still a fair distance out, and it looks marginal whether you
> are going to reach the runway or not.
>
> One technique I have sometimes heard described is to dive for
> the deck and complete the remaining distance in ground effect.
> For the sake of the argument we can assume fairly flat ground,
> free of obstacles, though not necessarily landable.
>
> The advantages claimed are usually better glide performance in
> ground effect and less headwind and absence of downdrafts close
> to the ground.
>
> On the other hand you'll be travelling at higher than optimal
> airspeed for most of the distance.
>
> I am wondering how much truth there actually is to this
> technique. Would it significantly increase your range and
> improve your chances of reaching the field or not ?
>
> Would it perhaps work better against a strong wind gradient
> (as I suspect it might), and maybe not help a lot in calm
> conditions ?
>
> I'd be interested in any hard data/analysis or otherwise
> enlightening comments on this.
>
> Please note though, that I am not talking about high-speed
> competition finishes, rounded off with a beatup and a sharp
> pullup and all the dangers and other issues involved in that.
>
> Cheers CV
>

[Bill Daniels]

The R-7755 had nine 4-cylinder inline water cooled blocks arranged around a
crankcase with a 4 throw crank. The liquid cooled radial was intended for
the pusher configurations of the B-35 and B-36. Engines intended for these
aircraft had an integral contra-rotating propeller gearbox in the nose case.
This is the configuration of the XR-7755 on display at the Air and Space
Museum.

The HK-1 was a tractor installation but liquid cooling would still have been
useful, particularly at high power settings used for water takeoff. Engines
for the HK-1 were to be single rotation.

These were VERY advanced engines with overhead cams, 4 valves/cyl, variable
valve timing and would eventually have had turbo-compounding.

Only the B-36 went on to production but with the 4360's it was so
underpowered that 4 jet engines were added. Had it used the R7755's no jets
would have been needed. Convair didn't design the B-36 to be underpowered,
they were forced to use the Pratt. Even so, I fondly remember the
earthshaking B-flat drone of a B-36.

The most interesting of these giants was the radar stealthy Northrop B-35
flying wing. This was the propeller version that was succeeded by the jet
B-49. With 40,000 HP, the B-35 would have been the fastest, longest range
prop bomber of all time even considering the turboprop TU95 Bear. It could
have carried more then 50,000 pounds of bombs to Europe and returned to
bases in North America. But, like Convair, Northrop was forced to use the
P&W 4360.

The cover story that the B35/B49 were cancelled because of "directional
instability" that made precision bombing impossible was nonsense. Just how
accurate do you have to be with a nuclear weapon? The real reason was that
the nuclear weapons of the time wouldn't fit in the Northrop's bomb bays.
Canceling the bomber for that reason would have tipped the Soviets to the
size of US weapons. Size and weight of nuclear bombs was top secret since
the first generation of ICBMs were then under development. The Northrop
flying wings were dead stable about all axes.

The history makes you appreciate the guts of the Smithsonian to put the
XR-7755 on display at all.

Bill Daniels

"John Sinclair" > wrote in message
...
> Bill,
> If memory serves me right the 4360 had 4 rows of 9
> cylinders for a total of 36 jugs. The aft rows were
> spiraled to allow cooling to the rear rows, but even
> so, the fourth row would run hotter. (KC-97F --circa
> 1952)
> What was the configuration of the 7755?
>
>
>
> At 13:48 19 October 2004, Bill
> >Lycoming engineers were confident that the R-7755 could
> >be developed to
> >produce 10,000 HP.
>
>
>

[Ralph Jones]

On Tue, 19 Oct 2004 21:50:52 GMT, "Bill Daniels" >
wrote:

>
>The history makes you appreciate the guts of the Smithsonian to put the
>XR-7755 on display at all.
>
After the crow they had to eat on the Wright/Langley affair, I imagine
they had no intention of colluding in any more coverups.

rj

[CV]

Daniel wrote:
> CV, a group of test pilot trainees at Edwards AFB did an exhaustive
> test on ground effect versus distance as a project during their
> course; it was reported in the Feb 1990 SOARING magazine. IIRC, they
> found that one had to fly a very precise profile - 0.95g push followed
> by 1.05g pull, to a precise height - to see any measurable effect, and
> concluded that it was better for the casual flier to fly best
> lift/drag speed instead... I think they used a G103. The notation

I see. So if the results as reported here apply to calm conditions
it would mean the ground-effect technique wins out whenever there
is any significant wind gradient.

Where there is wind there is usually a wind gradient, certainly
in strong winds, meaning the ground-effect technique would normally
win against a headwind.

As I said before I totally agree about the security issues. If
you end up in a position where you need this something is already
badly wrong. And if you have the option it would be better to
pick a field you are certain you can reach rather than rely on
these effects.

CV

[Kirk Stant]

CV > wrote in message >...

> I see. So if the results as reported here apply to calm conditions
> it would mean the ground-effect technique wins out whenever there
> is any significant wind gradient.
>
> Where there is wind there is usually a wind gradient, certainly
> in strong winds, meaning the ground-effect technique would normally
> win against a headwind.
>
> As I said before I totally agree about the security issues. If
> you end up in a position where you need this something is already
> badly wrong. And if you have the option it would be better to
> pick a field you are certain you can reach rather than rely on
> these effects.
>
> CV

Actually, no. If I remember correctly, the test concluded that in
order to achieve any noticeable benefit from ground effect, the glider
had to be flown extremely precisely at VERY low altitude - only a
couple of feet above the ground. None of this "half a wingspan" - so
unless you are stetching your glide over the Bonneville salt flats,
just keeping out of the usual bushes, fences, stray airport dogs, etc
would eliminate any ground effect benefit.

If the wind gradient is that strong, the turbulence at ground level
would make any precise low flying sporting and inefficient, anyway.

I think pilots confuse the distance a glider will "float in ground
effect" (with the dive brakes closed) with the simple low drag glide
angle as the glider slows down - and if over the runway this may be
helped a little by ground effect, but remember this "float to the end
of the runway" is usually started at a relatively low speed, so the
drag penalty of diving down to a high speed is not felt.

Try a constant altitude decelleration from Vne to Vstall at altitude
some time; it's amazing how long and far you go! (helps when you get
above the MSH...yeah I know you're not supposed to do it!)

Kirk

[CV]

Kirk Stant wrote:
> CV > wrote in message >...

>>I see. So if the results as reported here apply to calm conditions
>>it would mean the ground-effect technique wins out whenever there
>>is any significant wind gradient.

> Actually, no. If I remember correctly, the test concluded that in
> order to achieve any noticeable benefit from ground effect, the glider
> had to be flown extremely precisely at VERY low altitude - only a

I should have worded that differently.

What makes the difference there is less headwind close to
the ground. The ground effect would of course not increase
on account of the wind gradient.

> couple of feet above the ground. None of this "half a wingspan" - so
> unless you are stetching your glide over the Bonneville salt flats,
> just keeping out of the usual bushes, fences, stray airport dogs, etc
> would eliminate any ground effect benefit.

With bushes and fences it's not on. I was thinking more along the
lines of a big plowed field, perhaps with some ditches crossing
and maybe just a low fence between the field and the runway.

If there is some ground-effect benefit at 2 ft though, it won't
be magically "eliminated" at 2,5 ft. The effect will decrease
gradually with height.

> If the wind gradient is that strong, the turbulence at ground level
> would make any precise low flying sporting and inefficient, anyway.

It doesn't have to be very turbulent there. We are assuming
flat ground. When the gradient is strong the surface wind is
much weaker than winds aloft. That is the meaning of "gradient".

> I think pilots confuse the distance a glider will "float in ground
> effect" (with the dive brakes closed) with the simple low drag glide
> angle as the glider slows down - and if over the runway this may be
> helped a little by ground effect,

The slowing down factor is a valid point. And ground effect may
help a little, or more than a little, if it is true that it can
doube the L/D as someone mentioned.

but remember this "float to the end
> of the runway" is usually started at a relatively low speed, so the
> drag penalty of diving down to a high speed is not felt.
>
> Try a constant altitude decelleration from Vne to Vstall at altitude
> some time; it's amazing how long and far you go! (helps when you get
> above the MSH...yeah I know you're not supposed to do it!)

I suspect at altitude I wouldn't be able to appreciate the exact
distance covered and fail to be amazed.

CV

[Kirk Stant]

CV > wrote in message >...
>
> What makes the difference there is less headwind close to
> the ground. The ground effect would of course not increase
> on account of the wind gradient.

I would bet that if the wind is stong enough to have a strong
gradient, then there will be enough residual wind (and turbulence)
down low to affect the ability to stay low enough to use ground effect
- ever tried a high speed low pass on a windy day? It can be scary!

> With bushes and fences it's not on. I was thinking more along the
> lines of a big plowed field, perhaps with some ditches crossing
> and maybe just a low fence between the field and the runway.

The obvious way to check this assumption is to test it with two
gliders - start off in formation, co-speed, on final; then one glider
dives into "ground effect" and the other stays at L/D max. Both land
at minimum speed. Repeat a few times, alternating who does what, and
examine the results.

> If there is some ground-effect benefit at 2 ft though, it won't
> be magically "eliminated" at 2,5 ft. The effect will decrease
> gradually with height.

Apparently the drop off isn't gradual, but rapid - so it may be
significant at 2 feet, but insignificant at 5 feet. The Soaring
article gets into this, I think.

> It doesn't have to be very turbulent there. We are assuming
> flat ground. When the gradient is strong the surface wind is
> much weaker than winds aloft. That is the meaning of "gradient".

Again, if the "gradient" is that strong (and we are talking about the
area up to say 200' above the surface, not 1000'), then there is
likely some surface wind also - especially over smooth terrain that
would favor ground effect?

> The slowing down factor is a valid point. And ground effect may
> help a little, or more than a little, if it is true that it can
> doube the L/D as someone mentioned.

Russian work with Wing-In-Ground Effect (WIG) aircraft is fascinating
(also some German work in the area, and Boeing has a concept for a
huge WIG cargo plane, called the Pelican). Size seems to help, and
the ground effect was augmented by directing jet engine exhaust under
the wing. Double the L/D may be true, but likely only when inches
above the runway!

> I suspect at altitude I wouldn't be able to appreciate the exact
> distance covered and fail to be amazed.

Easy to do - just time how long it takes to slow down, then it is
pretty easy to approximate the distance. Or use a logger trace. I
tried it once in my LS6 at 8600', starting at 140 knots IAS and
slowing to 50 knots, trying to stay at the same altitude the whole
time (top of the start cylinder was 8600' - surprise!) Note that I
did this several miles outside the cylinder, flying towards it. I
know that it took at least 2 minutes to slow down (a very rough
number, since this was a real impromptu test, and 2 minutes was the
important number for me, for obvious reasons). So that is what? 2-3
miles? I'm sure there is a math whiz who can do the aero math to give
us the theoretical distance it should go.

IMHO, this idea (diving into ground effect) is like the idea that wet
pullups go higher - obvious, but incorrect.

Kirk

[Mark James Boyd]

It strikes me that an additional benefit of this (assuming you
don't hit anything early on) is that at the point
one perhaps inadvertently stalls, one is quite low (2 feet?)

The fatal accidents I've read commonly involve either stalls at
above 2 feet and/or hitting a wing first (not a wings-level touchdown).

In article >,
CV > wrote:
>Kirk Stant wrote:
>> CV > wrote in message >...
>
>>>I see. So if the results as reported here apply to calm conditions
>>>it would mean the ground-effect technique wins out whenever there
>>>is any significant wind gradient.
>
>> Actually, no. If I remember correctly, the test concluded that in
>> order to achieve any noticeable benefit from ground effect, the glider
>> had to be flown extremely precisely at VERY low altitude - only a
>
>I should have worded that differently.
>
>What makes the difference there is less headwind close to
>the ground. The ground effect would of course not increase
>on account of the wind gradient.
>
>> couple of feet above the ground. None of this "half a wingspan" - so
>> unless you are stetching your glide over the Bonneville salt flats,
>> just keeping out of the usual bushes, fences, stray airport dogs, etc
>> would eliminate any ground effect benefit.
>
>With bushes and fences it's not on. I was thinking more along the
>lines of a big plowed field, perhaps with some ditches crossing
>and maybe just a low fence between the field and the runway.
>
>If there is some ground-effect benefit at 2 ft though, it won't
>be magically "eliminated" at 2,5 ft. The effect will decrease
>gradually with height.
>
>> If the wind gradient is that strong, the turbulence at ground level
>> would make any precise low flying sporting and inefficient, anyway.
>
>It doesn't have to be very turbulent there. We are assuming
>flat ground. When the gradient is strong the surface wind is
>much weaker than winds aloft. That is the meaning of "gradient".
>
>> I think pilots confuse the distance a glider will "float in ground
>> effect" (with the dive brakes closed) with the simple low drag glide
>> angle as the glider slows down - and if over the runway this may be
>> helped a little by ground effect,
>
>The slowing down factor is a valid point. And ground effect may
>help a little, or more than a little, if it is true that it can
>doube the L/D as someone mentioned.
>
> but remember this "float to the end
>> of the runway" is usually started at a relatively low speed, so the
>> drag penalty of diving down to a high speed is not felt.
>>
>> Try a constant altitude decelleration from Vne to Vstall at altitude
>> some time; it's amazing how long and far you go! (helps when you get
>> above the MSH...yeah I know you're not supposed to do it!)
>
>I suspect at altitude I wouldn't be able to appreciate the exact
>distance covered and fail to be amazed.
>
>CV
>


--

------------+
Mark J. Boyd